The present invention relates to a sliding member used for a connecting rod for example, of which a sliding surface is subjected to a high surface load.
An engine used in an automobile, etc., converts up-and-down motion of a piston caused by explosion power of petroleum base fuel into rotational movement through a connecting rod and a crankshaft, to provide rotational driving power. The piston, connecting rod, crankshaft or the like are connected with each other through a shaft accommodated in a bearing, and a sliding surface of the bearing is repeatedly subjected to a rapidly increasing high load from the shaft as a mating member, during operation of the engine.
However, when the mating member and the bearing slide relative to each other in the state that the rapidly increasing high load is applied on the sliding surface, a lubricating oil film (or an oil film) retained on the sliding surface is broken to cause so-called partial metallic contact therebetween. Accordingly, there is a need of enhancing oil-film maintaining performance of the sliding surface of the bearing under such working environment, so as to prevent the lubricating oil from being flipped from the sliding surface even if the high load is applied thereto when the sliding surface slides on the mating member.
Although it is not directly related to the present invention, there has been proposed a sliding member in which an oil retaining property of a sliding surface is ensured by covering a bearing alloy layer with an overlay layer, and by blowing hard particles directly on the overlay layer to form fine holes on the overlay layer serving as the sliding surface, as shown in JP-A-2002-147459 (see paragraphs “0010” to “0034”, and TABLE 4), for example.
However, in the case of the sliding member disclosed in JP-A-2002-147459, the holes are formed by the blowing hard particles having an average particle size of 20 to 100 μm directly against the overlay layer, so that each hole has a so-called bowl shape and further, there is a tendency that the holes are not independent from one another but are contiguous to one another. According to this structure, in the case that the sliding surface slides in a state that a mating member applies a relatively low load on the sliding surface, lubricating oil is retained on the sliding surface by the holes formed on the overlay layer, so that an oil film is formed between the mating member and the sliding member (or between sliding surfaces).
However, in the case of a sliding member used for supporting a connecting rod, for example, a rapidly increasing high load is often generated on a part of its sliding surface. Under such working condition, since each of the holes for retaining the lubricating oil of the sliding member disclosed in JP-A-2002-147459 has a bowl-shape, the lubricating oil is easily flipped from the respective holes and flows out from a hole to a hole by virtue of the holes being contiguous to one another, so that it becomes difficult to maintain the oil film between the sliding surfaces, after all.